Size of Brain Structure Could Signal Vulnerability to Anxiety Disorders

Anxiety Disorders

Area appears smaller in those that continue to react to images associated with discomfort

The size of a particular structure in the brain may be associated with the ability to recover emotionally from traumatic events. A new study by researchers from Massachusetts General Hospital (MGH) finds that an area called the ventromedial prefrontal cortex is thicker in volunteers who appear better able to modify their anxious response to memories of discomfort. The report will appear in the Proceedings of the National Academy of Science and has received early online release on the PNAS website.

"We've always wondered why some people who are exposed to traumatic experiences go on to develop anxiety disorders like post-traumatic stress disorder and others do not," says Mohammed Milad, PhD, a research fellow in the MGH Department of Psychiatry, the study's lead author. "We think this study provides some potential answers."

In the classical model of conditioned fear, individuals respond with physical and emotional distress to situations that bring back memories of traumatic events. Such responses are normal and usually diminish over time, as those situations are repeated without unpleasant occurrences. But some people continue to respond with what can be overwhelming fear and may develop post-traumatic stress disorder (PTSD).

For example, it would not be unusual for a soldier who experienced a traumatic battlefield situation to become distressed when hearing noises that bring back those memories, such as the sound of a helicopter. Most commonly, repeated exposure to such sounds without additional trauma reduces or extinguishes the fearful response - a phenomenon called "extinction memory." But some individuals continue to experience anxiety, along with other symptoms characteristic of PTSD, when hearing the sounds.

Prior studies in animals have suggested that the ventromedial prefrontal cortex (vmPFC), an area on the lower surface of the brain, may be involved in extinction memory. The vmPFC may help to quell potential fears by inhibiting the activity of the amygdala, an area known to be involved with fear. The current study was designed to see if the structure of the vmPFC is related to the ability to modify response to an unpleasant memory.

Advertisement

Over a period of two days, 14 volunteer study participants viewed a series of digital photos of two different rooms. Each room contained a lamp that was turned on - sometimes with a red light, sometimes a blue light. On the first day, participants viewed the photos several times, and then viewed them again with a mild electric shock - described as annoying but not painful - delivered to their hands right after a lamp with a blue light appeared. They then viewed a series of the photos with no shocks administered.

On the second day, measurements of skin conductance were taken while the volunteers once again viewed the photos with both colors of lights displayed but no shocks given. A measurement of anxiety level, skin conductance is determined by the amount of perspiration on the palm of the hand. After that part of the experiment, the volunteers had structural magnetic resonance (MR) images taken of their entire brains.

The MR studies showed that those participants who appeared to have less anxiety response upon viewing the blue lights the second day, as measured by skin conductance, also had a thicker vmPFC. "That was the only area of the brain that correlated with extinction memory," says Milad. "So, these results suggest that a bigger vmPFC may be protective against anxiety disorders or that a smaller one may be a predisposing factor. But exactly how that might work we just don't know."

Scott Rauch, MD, the senior author of the paper and director of the Psychiatric Neuroscience Research Division in MGH Psychiatry, notes that future research could look at genetic or environmental factors that may underlie these differences in brain structure and also investigate whether vmPFC size predicts the success of exposure-based therapies for anxiety disorders. Another factor to study would be whether vmPFC measurement should be used to screen those likely to be exposed to traumatic situations or to develop preventive strategies. Rauch is an associate professor of Psychiatry at Harvard Medical School.

The report's co-authors are Roger Pitman, MD, of MGH Psychiatry; Brian Quinn and Bruce Fischl, PhD, of MGH Radiology, and Scott Orr, PhD, of the VA Medical Center in Manchester, N.H. The study was supported by grants from the National Institute of Mental Health and the MGH Tosteson Fellowship.

Massachusetts General Hospital, established in 1811, is the original and largest teaching hospital of Harvard Medical School. The MGH conducts the largest hospital-based research program in the United States, with an annual research budget of more than $450 million and major research centers in AIDS, cardiovascular research, cancer, cutaneous biology, medical imaging, neurodegenerative disorders, transplantation biology and photomedicine. In 1994, MGH and Brigham and Women's Hospital joined to form Partners HealthCare System, an integrated health care delivery system comprising the two academic medical centers, specialty and community hospitals, a network of physician groups, and nonacute and home health services.

Related Terms

Echinacea augustifolia is one of the most powerful healing herbs known to mankind. The first health benefit commonly attributed to Echinacea is its immune boosting ability, but there are many more health benefits that Echinacea has to offer beyond what you may have ever realized.

This morning in one of the ADHD groups I read this message from a mother of an ADHD child, which was very emotional and she is looking for help on how to handle difficult mornings. For the respect of her privacy I will not disclose her name, but here is the message and it's so common with many parents who raise children with ADHD. What would you advise her?

A house full of children is a house full of chaos. With our tablets and phones, Netflix and Minecraft, with our Amazon Echo, our radios and TVs, with a barking dog and sibling squabbles we are constantly in a state of massive over-stimulation. One day last month, it became abundantly clear to me that I had simply had ENOUGH.

Toxoplasma gondii is the parasite that causes toxoplasmosis. This parasitical infection is largely asymptomatic, but its been known to cause chronic oxidative stress in the brain of the host, which plays an essential role in the pathogenesis of neurological disorders like autism and ADHD.

Treatment for ADHD can involve tackling multiple areas of the brain in order to stimulate an improvement in cognition and the biomarkers of an ADHD diagnosis. Neurofeedback training has been tested as one possible treatment for ADHD patients, and found to improve many deficient or impaired areas in cognition, by regulating theta and beta wave activity.